Introduce a mangling for multiple opaque types within the declaration.

The `Qr` mangling is used to refer to the opaque type within the
declaration that produces the opaque type. When there are multiple
opaque types, e.g., due to structural or named opaque result types, it
does not specify which of the opaque type parameters it refers to.

Introduce a new mangling `QR INDEX` for opaque type parameters after
the first, retaining the `Qr` mangling for the first opaque type
parameter. This way, existing (non-structural) uses of opaque result
types retain the same manglings, but uses of structural or named
opaque result types (new features) will have distinct manglings.

Note that this mangling within a declaration is only used for the
declaration itself, and not for references to the opaque type of the
declaration, so there is no impact on the runtime demangler.

Author: DougGregor

docs/ABI/Mangling.rst

@@ -737,15 +737,17 @@ implementation details of a function type.
 ::
 
   #if SWIFT_VERSION >= 5.1
-    type ::= 'Qr'                         // opaque result type (of current decl)
+    type ::= 'Qr'                         // opaque result type (of current decl, used for the first opaque type parameter only)
+    type ::= 'QR' INDEX                   // same as above, for subsequent opaque type parameters, INDEX is the ordinal -1
     type ::= opaque-type-decl-name bound-generic-args 'Qo' INDEX // opaque type
 
     opaque-type-decl-name ::= entity 'QO' // opaque result type of specified decl
   #endif
 
   #if SWIFT_VERSION >= 5.4
-    type ::= 'Qu'                         // opaque result type (of current decl)
+    type ::= 'Qu'                         // opaque result type (of current decl, first param)
                                           // used for ObjC class runtime name purposes.
+    type ::= 'QU' INDEX
   #endif
 
 Opaque return types have a special short representation in the mangling of

include/swift/Demangling/DemangleNodes.def

@@ -329,5 +329,8 @@ NODE(AsyncSuspendResumePartialFunction)
 // Added in Swift 5.6
 NODE(AccessibleFunctionRecord)
 
+// Added in Swift 5.7
+NODE(OpaqueReturnTypeIndexed)
+
 #undef CONTEXT_NODE
 #undef NODE

lib/AST/ASTMangler.cpp

@@ -1318,7 +1318,10 @@ void ASTMangler::appendType(Type type, GenericSignature sig,
       auto opaqueDecl = opaqueType->getDecl();
       if (opaqueDecl->getNamingDecl() == forDecl) {
         assert(opaqueType->getSubstitutions().isIdentity());
-        return appendOperator("Qr");
+        if (opaqueType->getOrdinal() == 0)
+          return appendOperator("Qr");
+
+        return appendOperator("QR", Index(opaqueType->getOrdinal() - 1));
       }
 
       // Otherwise, try to substitute it.
@@ -1358,7 +1361,8 @@ void ASTMangler::appendType(Type type, GenericSignature sig,
         addTypeSubstitution(nestedType, sig);
         return;
       }
-      
+
+      // FIXME: Never actually used.
       appendType(nestedType->getParent(), sig, forDecl);
       appendIdentifier(nestedType->getName().str());
       appendOperator("Qa");

lib/Demangling/Demangler.cpp

@@ -2206,6 +2206,12 @@ NodePointer Demangler::demangleArchetype() {
   case 'r': {
     return createType(createNode(Node::Kind::OpaqueReturnType));
   }
+  case 'R': {
+    int ordinal = demangleIndex();
+    if (ordinal < 0)
+      return NULL;
+    return createType(createNode(Node::Kind::OpaqueReturnTypeIndexed, ordinal));
+  }
 
   case 'x': {
     NodePointer T = demangleAssociatedTypeSimple(nullptr);

lib/Demangling/NodePrinter.cpp

@@ -568,6 +568,7 @@ class NodePrinter {
     case Node::Kind::OpaqueType:
     case Node::Kind::OpaqueTypeDescriptorSymbolicReference:
     case Node::Kind::OpaqueReturnType:
+    case Node::Kind::OpaqueReturnTypeIndexed:
     case Node::Kind::OpaqueReturnTypeOf:
     case Node::Kind::CanonicalSpecializedGenericMetaclass:
     case Node::Kind::CanonicalSpecializedGenericTypeMetadataAccessFunction:
@@ -2817,6 +2818,7 @@ NodePointer NodePrinter::print(NodePointer Node, unsigned depth,
     Printer << ")";
     return nullptr;
   case Node::Kind::OpaqueReturnType:
+  case Node::Kind::OpaqueReturnTypeIndexed:
     Printer << "some";
     return nullptr;
   case Node::Kind::OpaqueReturnTypeOf:

lib/Demangling/OldDemangler.cpp

@@ -2078,6 +2078,13 @@ class OldDemangler {
         // Special mangling for opaque return type.
         return Factory.createNode(Node::Kind::OpaqueReturnType);
       }
+      if (Mangled.nextIf('U')) {
+        // Special mangling for opaque return type.
+        Node::IndexType ordinal;
+        if (!demangleIndex(ordinal, depth))
+          return nullptr;
+        return Factory.createNode(Node::Kind::OpaqueReturnTypeIndexed, ordinal);
+      }
       return demangleArchetypeType(depth + 1);
     }
     if (c == 'q') {

lib/Demangling/OldRemangler.cpp

@@ -2643,6 +2643,11 @@ ManglingError Remangler::mangleOpaqueReturnType(Node *node, unsigned depth) {
   Buffer << "Qu";
   return ManglingError::Success;
 }
+ManglingError Remangler::mangleOpaqueReturnTypeIndexed(Node *node, unsigned depth) {
+  Buffer << "QU";
+  mangleIndex(node->getIndex());
+  return ManglingError::Success;
+}
 ManglingError Remangler::mangleOpaqueReturnTypeOf(Node *node,
                                                   EntityContext &ctx,
                                                   unsigned depth) {

lib/Demangling/Remangler.cpp

@@ -3280,6 +3280,11 @@ ManglingError Remangler::mangleOpaqueReturnType(Node *node, unsigned depth) {
   Buffer << "Qr";
   return ManglingError::Success;
 }
+ManglingError Remangler::mangleOpaqueReturnTypeIndexed(Node *node, unsigned depth) {
+  Buffer << "QR";
+  mangleIndex(node->getIndex());
+  return ManglingError::Success;
+}
 ManglingError Remangler::mangleOpaqueReturnTypeOf(Node *node, unsigned depth) {
   RETURN_IF_ERROR(mangle(node->getChild(0), depth + 1));
   Buffer << "QO";

test/IRGen/opaque_result_type.swift

@@ -188,7 +188,7 @@ public func useFoo(x: String, y: C) {
   let _ = bauble(z: y, u: y)
 }
 
-// CHECK-LABEL: define {{.*}} @"$s18opaque_result_type6bauble1z1uSayQr_QrSgtGx_q_tAA6MarkerRzAA1PRzAA1QRzAaIR_r0_lF"
+// CHECK-LABEL: define {{.*}} @"$s18opaque_result_type6bauble1z1uSayQr_QR_SgtGx_q_tAA6MarkerRzAA1PRzAA1QRzAaIR_r0_lF"
 
 // CHECK-LABEL: define {{.*}} @"$s18opaque_result_type6useFoo1x1yySS_AA1CCtF"
 // CHECK: [[OPAQUE:%.*]] = call {{.*}} @"$s18opaque_result_type3baz1zQrx_tAA1PRzAA1QRzlFQOMg"
@@ -203,7 +203,7 @@ struct Boom<T: P> {
 }
 
 // CHECK-LABEL: define {{.*}} @"$s18opaque_result_type9gimmeBoomypyF
-// CHECK: call swiftcc void @"$s18opaque_result_type4BoomV5prop15prop2ACyxGSi_AcEQr_QrtvpQOyx_Qo__AcEQr_QrtvpQOyx_Qo0_ttcfcfA0_"
+// CHECK: call swiftcc void @"$s18opaque_result_type4BoomV5prop15prop2ACyxGSi_AcEQr_QR_tvpQOyx_Qo__AcEQr_QR_tvpQOyx_Qo0_ttcfcfA0_"
 public func gimmeBoom() -> Any {
   Boom<String>(prop1: 5)
 }

test/IRGen/opaque_result_type_debug.swift

@@ -68,9 +68,9 @@ public func bar<T: P>(genericValue: T) {
 // CHECK-DAG: {{![0-9]+}} = !DILocalVariable(name: "opaqueValue",{{.*}} type: ![[LET_OPAQUE_TYPE]])
 // CHECK-DAG: {{![0-9]+}} = !DILocalVariable(name: "opaquePropValue",{{.*}} type: ![[LET_OPAQUE_PROP_TYPE]])
 // CHECK-DAG: {{![0-9]+}} = !DILocalVariable(name: "opaqueSubValue",{{.*}} type: ![[LET_OPAQUE_SUB_TYPE]])
-// CHECK-DAG: ![[OPAQUE_ARRAY_FIRST_TYPE:[0-9]+]] = !DICompositeType({{.*}} name: "$s30opaque_result_type_debug_other3barSayQr_QrSgtGyFQOyQo_D"
+// CHECK-DAG: ![[OPAQUE_ARRAY_FIRST_TYPE:[0-9]+]] = !DICompositeType({{.*}} name: "$s30opaque_result_type_debug_other3barSayQr_QR_SgtGyFQOyQo_D"
 // CHECK-DAG: ![[LET_OPAQUE_ARRAY_FIRST_TYPE:[0-9]+]] = !DIDerivedType(tag: DW_TAG_const_type, baseType: ![[OPAQUE_ARRAY_FIRST_TYPE]])
 // CHECK-DAG: {{![0-9]+}} = !DILocalVariable(name: "opaqueArrayFirst",{{.*}} type: ![[LET_OPAQUE_ARRAY_FIRST_TYPE]])
-// CHECK-DAG: ![[OPAQUE_ARRAY_SECOND_TYPE:[0-9]+]] = !DICompositeType({{.*}} name: "$s30opaque_result_type_debug_other3barSayQr_QrSgtGyFQOyQo0_D"
+// CHECK-DAG: ![[OPAQUE_ARRAY_SECOND_TYPE:[0-9]+]] = !DICompositeType({{.*}} name: "$s30opaque_result_type_debug_other3barSayQr_QR_SgtGyFQOyQo0_D"
 // CHECK-DAG: ![[LET_OPAQUE_ARRAY_SECOND_TYPE:[0-9]+]] = !DIDerivedType(tag: DW_TAG_const_type, baseType: ![[OPAQUE_ARRAY_SECOND_TYPE]])
 // CHECK-DAG: {{![0-9]+}} = !DILocalVariable(name: "opaqueArraySecond",{{.*}} type: ![[LET_OPAQUE_ARRAY_SECOND_TYPE]])